The mother of an Alabama boy held for days in an underground bunker says she forgave her son's captor early in the standoff and asked authorities not to harm him.

Jennifer Kirkland's son, Ethan, was a captive for six days in rural Midland City, Alabama, before FBI agents entered the bunker and killed 65-year-old Jimmy Lee Dykes. Authorities said Dykes had snatched Ethan off a school bus after fatally shooting the driver.

Dykes "took care of Ethan to the best of his abilities" by cooking chicken for the boy and asking hostage negotiators to bring the child his favourite toy car, his mother told Dr Phil McGraw in an interview for the Dr Phil Show.

"From the very beginning I had already forgiven Mr Dykes, even though he still had my child," Kirkland said. "...I asked that he not be hurt. But if it came down to it, you know, of course I want my child safe."

Authorities returned Ethan unharmed after a gunbattle in which Dykes, according to a coroner, was shot multiple times. Kirkland said her son, who turned six just two days after the rescue, told her that he witnessed the shooting.

Members of the rescue team used stun grenades to disorient Dykes, who had a gun and had become agitated with negotiators, before rushing into the bunker, she said.

"They went in and covered Ethan with a vest and they shot Mr. Dykes," Kirkland said.

Ethan saw the agents kill his captor, his mother said, just as days earlier he had witnessed Dykes storm onto his school bus and fatally shoot the driver, Charles Albert Poland Jr.

Poland and Ethan had become close, Kirkland said, as the driver had helped the boy work up the courage to get off the bus by himself.

"Ethan has always been scared of coming down the bus steps," Kirkland said. "And Mr Poland would always cheer him on, you know, 'come on, little buddy, you can do it'."

Ethan typically sat right behind Poland on the school bus, where the driver could keep an eye on him, Kirkland said.

That's where the boy was sitting the day police say Dykes came aboard the bus armed with a gun and demanding two hostages. Authorities say Poland was shot trying to stand between Dykes and the children.

"The reason I think Ethan was taken off the bus is because when he saw Mr Poland shot, Ethan passed out," Kirkland said. "Mr Dykes went down to catch him and he picked him up. And I think, in his own way, he was trying to care for him."

After the shooting, authorities say, Dykes fled to the bunker with the child as the standoff opened.